1. Field of the Invention
The invention pertains to a bridging clutch including a first converter component having a friction area and a friction lining carrier carrying a friction lining, wherein the friction lining and the friction area can be shifted into working connection by an engaging movement, the friction lining having radially inner side with at least one radially inward facing opening with an inflow area and an outflow area for the passage of transport medium.
2. Description of the Related Art
A bridging clutch for a hydrodynamic torque converter is known from U.S. 2003/010589. This bridging clutch has a piston, and as shown in FIG. 1, the side of this piston which faces the converter cover can be brought into working connection with a first friction lining, one side of which is attached to a plate connected nonrotatably to the turbine wheel of the torque converter. The plate carries on its opposite side, i.e., the side facing a converter cover, a second friction lining, which, like the first friction lining, serves as a friction area. The piston can be moved either toward the converter cover to engage the bridging clutch or in the opposite direction to disengage the clutch. As soon as the friction area of the first friction lining makes contact with the piston and the second friction lining makes contact with the converter cover, the contact surfaces of the piston and the converter cover serve as opposing friction areas. The piston acts as the first converter component, the converter cover as the second converter component, and the plate as the third converter component of the bridging clutch.
As soon as the bridging clutch is at least essentially engaged, a rotational movement of the converter housing around its axis of rotation is no longer transmitted via a hydrodynamic circuit within the pump wheel, the turbine wheel, and the stator to a transmission input shaft, but rather arrives directly at the shaft just mentioned via the bridging clutch.
The use of the bridging clutch may be advantageous from the standpoint of energy efficiency, but when it is in operation, the bridging clutch should also be used to damp any torsional vibrations that may be introduced along with the introduced torque. For this reason, the piston of a bridging clutch designed without a torsional vibration damper is relieved of some of the load being exerted on it by decreasing the pressing force directed toward the converter cover. This allows the clutch intentionally to slip, and although this may indeed serve to damp the introduced torsional vibrations effectively, it also allows a considerable amount of heat to build up in the friction area and in the opposing friction area. Measures must therefore be taken to ensure that the heat which thus develops can be removed as quickly as possible from the working area of the bridging clutch. In U.S. 2003/010589, this is accomplished by providing openings in the friction linings. As shown in FIG. 2, these openings are preferably designed in such a way that their outer radial contour extends essentially radially inward in opposite directions from a crest point and terminates in the radially inward direction at inflow and outflow areas. The inner radial contour of the openings, which are formed as grooves, copies the geometry of the outer radial contour. A groove-like opening formed in this way in a friction lining is referred to by experts in the field as an “arc groove”.
An investigation of these types of openings in the friction linings of bridging clutches led to the following conclusions:
As a result of the relative rotational movement between the converter component with the friction surface and the converter component with the opposing friction surface, transport medium flows into the associated inflow area of each opening and then continues toward the outflow area. Nevertheless, some of the transport medium will adhere both to the outer radial contour of the opening and to the inner radial contour, so that boundary layers with pronounced velocity gradients will form near the contours. Because of the difference between the velocity of the boundary layer at the outer radial contour and the velocity of the boundary layer at the inner radial contour, a vortex will form essentially in the outflow area of the opening, as studies have shown and as FIG. 5 of the present patent application illustrates on the basis of the state of the art. It is true that basically cool transport medium is concentrated in the area over which this vortex extends, and this should promote a very effective heat exchange. This vortex, however, at least narrows down the outflow area of the opening or possibly even blocks it completely. The result is that heated transport medium present in the opening cannot leave the opening via the outflow area at a fast enough rate, and accordingly it is impossible for cool transport medium to enter at the inflow area of the opening. Instead, most of this transport medium will pass by the opening on the radially inner side and, after flowing around the vortex mentioned, will proceed in the circumferential direction to the adjacent opening. It is obvious that the cooling effect therefore not only becomes highly irregular, but is also reduced to a minimum.